Newest Frontier in Cardiac Care: Kidneys

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 - Medtronic Symplicity renal denervation system
The Symplicity renal denervation system uses a catheter to deliver low-level radiofrequency energy through the renal artery wall. A physician inserts the catheter into the femoral artery to access the renal artery. A generator is then activated to deliver the energy.
Source: Medtronic

They say the way to a man’s heart is through his stomach. Not so, at least when it comes to cardiac care. Recent research and clinical practice point to the kidneys as a pathway for treating cardiovascular diseases. Using a percutaneous, catheter-based technique to disrupt overactive renal sympathetic nerves, specialists have been able to lower blood pressure in patients with drug-resistant hypertension. And they aren’t stopping there. Early studies show the approach may be effective for treating atrial fibrillation (AF) and heart failure (HF) as well. 

An unnerving scenario

The heart is one of several organs that in concert regulate blood pressure. The kidneys also play an important role, assisted by the renal sympathetic efferent and afferent nerves within and adjacent to the walls of the renal artery. If the nerves that feed into the sympathetic nervous system go into overdrive, then they may precipitate hypertension. Systemic hypertension, in turn, can cause organ damage and put hypertensive people at risk for major cardiovascular events such as stroke.

One-third of U.S. adults are hypertensive, according to the American Heart Association. Worldwide, that estimate grows to approximately one-quarter of adults, with prevalence expected to rise in developing countries. For many patients, medications can control their hypertension and reduce the risk of stroke. But some patients cannot achieve target blood pressure even when treated with many drug therapies at the highest tolerated doses.  

Renal denervation, an approach that uses percutaneous catheters and radiofrequency energy to disrupt renal nerve signaling, may prove to be an option for people with treatment-resistant hypertension. Because poorly controlled hypertension also is a risk factor for AF, electrophysiologists are exploring the use of renal denervation to reduce AF occurrences. Poor cardiac function also sets the sympathetic nervous system into overdrive, a condition that has cardiologists viewing renal denervation as a therapy in HF. 

“In medical school, we are taught that all of these diseases have separate etiologies; they all come from different sources,” says Justin E. Davies, MBBS, PhD, of the International Centre for Circulatory Health at the National Heart and Lung Institute at Imperial College London. “Actually, what this therapy may tell us is that they may have a common source, or at least that the effects of these diseases may be magnified by an increase in stress hormones.”

As early as the 1930s, physicians recognized that surgical renal denervation could reduce what was termed malignant hypertension (J Clin Invest 1935;14[1]:22-26). But the invasive procedure had long-term complications. Several decades later, the development of antihypertensive agents offered physicians an option for treating patients. But up to 30 percent of patients diagnosed with high blood pressure may fail to respond to three or more antihypertension drugs, says Markus Schlaich, MD, an investigator in Symplicity HTN-1, a clinical trial that assessed the safety and efficacy of renal denervation in patients with treatment-resistant hypertension.

“Treatment-resistant hypertension is something you encounter quite frequently in general practice,” says Schlaich, who also is head of the Neurovascular Hypertension & Kidney Disease Laboratory at Baker IDI Heart and Diabetes Institute in Melbourne, Australia.

Compare the costs

A model designed to assess the cost-effectiveness of renal denervation in resistant hypertensive patients estimated (2010 U.S. dollars):

  • One-time material and procedure costs for renal denervation of $12,500;
  • 30-day costs of stroke of
    $18,627;
  • First-year cost of heart failure of $14,532;
  • A discounted lifetime incremental cost-effectiveness ratio of $2,715 per life-year gained; and
  • 3,071 per quality-adjusted
    life year.

Source: J Am Coll Cardiol 2012;60(14):1271-1277.

Catheter-based renal denervation is a less invasive approach, but it is still in its infancy. In a proof-of-concept study, Schlaich and colleagues enrolled 50 treatment-resistant hypertensive patients from five centers in Europe and Australia between 2007 and 2008 with a one-year follow-up (Lancet 2009;373:1275-1281). The primary endpoints included office blood pressure and safety data. Ardian, maker of the device in the trial, sponsored the study. Medtronic acquired Ardian in 2010 and now sponsors the Symplicity trial.

Treated patients had a mean baseline office-based blood pressure of 177/101